1. Field of the Invention
The present invention generally relates to thermometers with components that react to changes in temperature by changing color, such as thermochromic liquid crystals (TLCs). More particularly, the invention concerns an apparatus or article of manufacture comprising a multi-colored decal such as an animal, flower, fish, or other design with spots or other features that individually reveal or display a message according to the ambient temperature. According to the decal's current temperature, an appropriate one of the temperature sensors, normally camouflaged within the features of the decal, is activated and thus becomes visible.
2. Description of the Related Art
Temperature sensing devices come in a variety of forms, with various underlying scientific principles. One recent type of thermometer uses TLCs, usually constructed in a planar shape. TLCs react to changes in temperature by changing color. These materials are made of twisted molecular structures comprising optically active mixtures of organic chemicals. TLCs include cholesteric compositions, chiral nematic formulations, and combinations of the two.
TLCs show colors by selectively reflecting incident white light. "Temperature-sensitive" mixtures in thin films reflect bright, almost pure colors. They turn from colorless (black, against a black background) to red at a given temperature, and pass through the other colors of the visible spectrum in sequence as temperature increases. This progression includes orange, yellow, green, blue, and violet. At an even higher temperature, the crystals turn colorless (black) again.
In contrast to temperature-sensitive mixtures, "temperature-insensitive" formulations reflect just a single color below a given transition temperature, changing to colorless (black) above this temperature. These formulations are sometimes called "shear-sensitive" or "clearing point" mixtures. TLC formulations have also been developed that provide a bandpass feature, reflecting a single color within a prescribed temperature range, otherwise changing to colorless (black).
TLCs have been implemented in a variety of forms. One of the most prevalent examples is a temperature strip made by placing numerous TLC rectangles end to end. The rectangles are arranged so that, as the ambient temperature changes from lowest to highest readable temperature, the rectangles are individually illuminated sequentially from one end of the strip to the other. This is done by using bandpass-type TLC rectangles with sequentially increasing activating temperatures. One example is the reversible temperature sensor, part A5321, manufactured by Hallcrest, Inc. of Glenview Ill. With this particular part, the TLC in each rectangle is shaped into numbers defining the corresponding temperature sensed by that rectangle, such as "74".
TLC materials are used in many different product configurations. For example, some temperature strips are attached to a background border printed with certain textual information. For example, the border may include evenly marked numerical increments of temperature, a temperature scale (e.g., Celsius) that contrasts with that shown on the temperature strip, etc. With other products, the border material includes a cartoon drawing, ruler, or other non-textual information. In some cases, the printed border design provides a decorative function unrelated to the temperature strip; in other configurations, the printed border provides data with some relation to the temperature strip.
Although some of the thermometers discussed above enjoy widespread commercial success today, the present inventors have sought to improve the utility and operation of known thermometers.